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United States Patent |
5,171,344
|
Noda
|
December 15, 1992
|
Method for manufacturing a gradient index optical element
Abstract
In accordance with the present invention, the dopant within one gradient
index optical element has two independent concentration distributions.
Particularly to use the present invention to obtain a gradient index
optical element having an excellent chromatic aberration correction
ability, it is only needed to make such dopant distributions as shown in
the previously stated Japanese Patent Application No. 280897/1989.
However, as to the doping of a dopant into a porous body, there is a limit
in the amount which can be doped. This is a disadvantage of the molecular
stuffing method, but the reason for this is that the dopant must be
supplied into the holes as a solution and it is largely restricted by the
solubility of the dopant in the solvent. In addition, since the intra-hole
fixing of the dopant depends on the solubility difference by temperature
or that by solvent exchange, it is further restricted. For this, the
latter process which is an application of the molecular stuffing method
preferably takes the distribution that has less doping amount.
Accordingly, a large concentration distribution must be provided to the
dopant in the preceding process. For that, the preceding process is
desirably a gel which has sufficiently large concentration gradient by the
sol-gel method. However, the sol-gel method also has a defect, in which
the distribution provision relies on the elution of the dopant metal, and
thus a convex distribution is easier to produce in principle.
In view of the foregoing, it is the most effective that the concentration
gradient of the first dopant is formed in a convex shape by the sol-gel
method using alcoxide as the raw material for retreiving the first dopant,
and that the concentration gradient of the second dopant is formed in a
concave shape by an application of the molecular stuffing method.
Inventors:
|
Noda; Satoshi (Akishima, JP)
|
Assignee:
|
Olympus Optical Company Limited (JP)
|
Appl. No.:
|
717417 |
Filed:
|
June 18, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
65/395; 65/30.1; 65/399; 65/415; 65/901; 385/124 |
Intern'l Class: |
C03C 025/02 |
Field of Search: |
65/3.11,3.12,3.14,3.15,18.1,18.2,30.1,30.13,901
385/124
359/654
|
References Cited
U.S. Patent Documents
4462663 | Jul., 1984 | Shimizu et al. | 359/654.
|
4478623 | Oct., 1984 | Olshansky | 65/3.
|
4563205 | Jan., 1986 | Asahara | 65/30.
|
4576836 | Mar., 1986 | Colmet et al. | 427/255.
|
4907864 | Mar., 1990 | Hagerty et al. | 359/654.
|
Primary Examiner: Lindsay; Robert L.
Attorney, Agent or Firm: Adams; Bruce L., Wilks; Van C.
Claims
What is claimed is:
1. A method for manufacturing a gradient index optical element, comprising
the steps:
forming a porous body having a first predetermined concentration
distribution due to a first dopant incorporated into said porous body;
dipping said porous body in a solution containing a second dopant to
establish in said porous body a second predetermined concentration
distribution due to said second dopant; and
fixing said first and second concentration distributions in said porous
body.
2. A method for manufacturing a gradient index optical element as set forth
in claim 1, wherein said first dopant is a material having ions including
at least bivalent ions.
3. A method for manufacturing a gradient index optical element as set forth
in claim 1, wherein said second dopant is a material having ions including
at least bivalent ions.
4. A method for manufacturing a gradient index optical element as set forth
in claim 2, wherein said porous body having said first predetermined
concentration distribution is a gel synthesized by a sol-bel method using
alcoxide as the raw material for receiving the first dopant.
5. A method for manufacturing a gradient index optical element as set forth
in claim 2, wherein said porous body having said first predetermined
concentration distribution is soot synthesized by a CVD method.
6. A method for manufacturing a gradient index optical element as set forth
in claim 3, wherein said porous body having said first predetermined
concentration distribution is gel synthesized by a sol-gel method using
alcoxide as the raw material for receiving the first dopant.
7. A method for manufacturing a gradient index optical element as set forth
in claim 3, wherein said porous body having said first predetermined
concentration distribution is soot synthesized by a CVD method.
8. A method for manufacturing a gradient index optical element as set forth
in claim 4, wherein the concentration of said first dopant gradually
becomes lower from the center of said porous body toward the outside
thereof, and the concentration of said second dopant gradually becomes
higher from the center of said porous body towards the outside thereof.
9. A method for manufacturing a gradient index optical element as set forth
in claim 5, wherein the concentration of said first dopant gradually
becomes lower from the center of said porous body toward the outside
thereof, and the concentration of said second dopant gradually becomes
higher from the center of said porous body towards the outside thereof.
10. A method for manufacturing a gradient index optical element as set
forth in claim 1, wherein the first dopant comprises at least one metal
selected from a group consisting of Ba, La, Sr, Ca, Ge, Zr, Y and Zn; and
the second dopant comprises at least one metal selected from a group
consisting of Ta, Nb, Pb, Ti, Bi, Zn, and Zr.
11. A method for manufacturing a gradient index optical element as set
forth in claim 1, wherein said porous body comprises a gel.
12. A method for manufacturing a gradient index optical element as set
forth in claim 1, wherein said porous body comprises soot.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a method for manufacturing gradient
index optical elements.
2. Prior Art
Gradient index optical elements have attracted attention because of their
excellent aberration correction ability as optics which are essential to
the next generation optical systems.
There are various gradient index optical elements which are being
researched and developed in many companies and research institutes,
including the SELFOC (a registered trademark) lens and slab lens which are
already available in the market.
In gradient index optical elements, their medium itself is provided with a
power (refractive power) by adding a refractive index distribution. The
power depends on the refractive index distribution, and it is only
necessary to increase the gradient difference of refractive index n
(hereinafter referred to as .DELTA.n) in order to increase the power.
Accordingly, at present, to increase the .DELTA.n is a large problem given
to the research and development of gradient index optical elements, and
many researchers are studying how to increase the .DELTA.n. For instance,
for the optics which are marketed under the name of SELFOC lens, the
.DELTA.n is increased by providing a concentration gradient of T1 by ion
exchange. Also, by providing a concentration gradient of Ag using a double
ion exchange method, a lens was obtained for which .DELTA.n.apprxeq.0.1
(the 28th Discussion on Glass).
In addition, by the sol-gel method, a lens for which .DELTA.n=0.04 was
obtained by providing concentration gradients of Pb and K (J. Non-cry.
sol. 100, 506, 1988), and a lens for which .DELTA.n=0.03 was obtained by
providing a concentration gradient of Ti or Ge (Elect. Lett, 22, 99
(1986), Elect. Lett, 22, 1108 (1986)).
Incidentally, the developments of gradient index optical elements up to the
present have mainly an approach of increasing the outer diameter, but the
measures to decrease the chromatic aberration possessed by the optics
themselves have been late. Since refractive index distribution type optics
have excellent aberration correction ability, it is possible to
drastically decrease the number of the constituent lenses, but there is an
inconsistency that the chromatic aberration correction of a lens system
becomes more difficult as the number of the lenses decreases. Accordingly,
to make a lens system which includes a gradient index optical elements and
has the chromatic aberration thereof fully corrected, it may be needed to
take measures such as addition of an achromatic lens depending on the
case, and thus the merit of the gradient index optical elements is reduced
by half.
Thus, to make a lens system in which the number of lenses is small and the
chromatic aberration is also corrected, it is important to decrease the
chromatic aberration itself generated in each lens and it is important to
decrease the chromatic aberration of the gradient index optical elements
itself. For this, the following characteristics are desired as the
characteristics required for the medium of gradient index optical
elements.
In radial gradient index optical elements, the refractive index of the
medium differs depending on the position through which a light beam is
passing (the distance from the axis), and hence the refractive index of
the light beam differs. If it is now supposed that the Abbe number
##EQU1##
of the medium is constant, then in a portion having a high refractive
index, the light beam as it passes through the medium largely refracts as
shown in FIG. 1 (a), so that the spread due to the difference in the
wavelength of the light beam becomes large as compared with a portion
having a low refractive index. That is, if the Abbe number .nu..sub.d is
fixed, the chromatic aberration (n.sub.F -n.sub.C) increases as the
refractive index n.sub.d increases. Consequently, in order to decrease the
chromatic aberration (n.sub.F -n.sub.C), it is desirable that the Abbe
number .nu..sub.d is large in the portion having a high refractive index
as shown in FIG. 1 (b). That is, the characteristics changing in the form
of high refractive index.multidot.low dispersion-low refractive
index.multidot.high dispersion are desirable as the characteristics of the
medium.
Also, axial gradient index optical elements can be considered similarly to
the conclusion obtained for the conventional achromatic junction lens
(tablet) shown in FIGS. 2 (a) and (b). Thus, in axial gradient index
optical elements, the junction of a high-refractive index medium lens with
a low-refractive index medium lens is achieved by providing the medium
with a refractive index distribution within the same lens as shown in
FIGS. 2 (c) and (d), and it is therefore desirable for the characteristics
to vary in the form of high refractive index.multidot.low dispersion-low
refractive index.multidot.high dispersion similarly to radial gradient
index optical elements. This indicates that optics whose optical
characteristics change in the direction A on the n.sub.d -.nu..sub.d graph
shown in FIG. 3 are more excellent in the point of chromatic aberration
correction than those having optical characteristics that change in the
direction B (refer to the Japanese Patent Application Laid-Open No.
218614/1985 official gazette).
However, few of the gradient index optical elements which are presently
being developed have such characteristics and even in those which have
already been actualized, .DELTA.n remains to be a very small value.
That is mainly caused by the manufacturing method of gradient index optical
elements. For instance, in the ion exchange method, in order to make
.DELTA.n large, a concentration gradient is provided by the ion exchange
between Tl.sup.+ ions having a valence of one, which are introduced into
glass so as to constitute a glass modification oxide (that is not directly
related to the glass formation), and N.sup.+ or K.sup.+ ions. But, the
use of Tl.sup.+ makes .DELTA.n large whereas the change characteristics
of the Abbe number becomes a high refractive index.multidot.high
dispersion-low refractive index.multidot.low dispersion type, and thus a
chromatic aberration will largely occur. Also, .DELTA.n can be made large
by the exchange of Ag.sup.+ with Na.sup.+, but a large chromatic
aberration will similarly occur.
In addition, there is an instance in which the chromatic aberration is
significantly improved using Li.sup.+, but on the other hand, .DELTA.n
becomes small and its effect is not fully exhibited. Although .DELTA.n can
be improved by increasing the content of Li.sup.+, there is a limit
because of the resistance of the glass body material and the difficulty of
the technique of stably dissolving the easily volatile alkali content into
the glass body material, and the one of a level which actually exhibits a
sufficient effect has not yet been obtained.
Since, in the ion exchange method, a concentration gradient can essentially
be provided only by positive ions having a valence of one because the
exchange speed of ions having a valence larger than one is extremely low,
the variations of the ion concentration gradient for providing the
distribution thereof are very limited, and thus the one has not yet been
achieved in which .DELTA.n is large and the occurrence of a chromatic
aberration is low as described above.
Further, the development by the sol-gel method is now proceeded with, and
there is a method wherein a metal element such as Ti, Ge or Zr which
enhances the refractive index and constitutes the glass forming oxide
(that is originally contained for forming glass) is eluted from a wet gel
by an acid or the like. In this method, the change characteristics of the
Abbe number are of the high refractive index.multidot.high dispersion-low
refractive index.multidot.low dispersion type though a .DELTA.n which is
large to some extent is obtained, and thus a chromatic aberration largely
occurs and the characteristics of the gradient index optical elements are
near to those obtained by the ion exchange of the Tl.sup.+ - Na.sup.+
type.
Also, in the Japanese Patent Publication No. 15492/1987 official gazette,
it is shown that chromatic aberration (dispersion) can be made small using
Nb, Ta, Sc, Y, La or Th as a dopant metal. However, this method has no
difference in that dispersion changes from a high dispersion to a low
dispersion as the refractive index changes from a high refractive index to
a low refractive index, and the amount of change in its dispersion value
is merely small. That is, since the dispersion is eventually shown by the
reciprocal of the Abbe number, the method described in the Japanese Patent
Publication No. 15492/1987 official gazette has no difference in that it
is the dispersion of the direction B in FIG. 3 of the specification of
this application, and its angle is merely made such that the arrow in the
figure stands.
Moreover, in the Japanese Patent Publication No. 6295/1985 official
gazette, a multiple-dope method is disclosed in which a molecular stuffing
method is repeated. But, this method had two problems that a .DELTA.n
which can practically be used is not obtained because of the small amount
of a dopant that can be doped at a time, and that it relies on an
impractical process in which a baking at a high temperature in a furnace
is performed for each doping.
The present invention was made in view of such prior art problems, and its
object is to provide a method for manufacturing gradient index optical
elements having various characteristics, including gradient index optical
elements having an excellent chromatic aberration correction ability, in
which .DELTA.n is large enough for practical use and the characteristics
change of the Abbe number is of a high refractive index.multidot.low
dispersion-low refractive index.multidot.high dispersion type.
SUMMARY OF THE INVENTION
In order to accomplish the above object, the method for manufacturing
gradient index optical elements has a process of forming a porous body
having a first predetermined concentration gradient due to a first dopant
incorporated into the porous body thereof and a process of dipping the
porous body in a solution containing a second dopant, thereby to provide
the porous body with a second predetermined concentration gradient due to
the second dopant.
In the method for manufacturing gradient index optical elements, the porous
body having the first predetermined concentration gradient may be a gel
synthesized by a sol-gel method using alcoxide as the raw material for
receiving the dopant, or soot synthesized by a CVD method for receiving
the dopant.
In the method for manufacturing gradient index optical elements, the first
predetermined concentration gradient may be such that the concentration of
the first dopant gradually becomes lower from the center of the porous
body toward the outside thereof, and the second predetermined
concentration gradient is such that the concentration of the second dopant
gradually becomes high from the center of the porous body toward the
outside thereof.
In the method for manufacturing gradient index optical elements of the
present invention having the above described construction, since a porous
body is formed which has a first predetermined concentration gradient due
to a first dopant previously incorporated into the porous body, the doping
amount of the first dopant can be made large, and thus .DELTA.n can be
made sufficiently large. In addition, in the present invention, since a
second predetermined concentration gradient due to a second dopant is
provided to the porous body having the first predetermined concentration
gradient by dipping the porous body in a solution containing the second
dopant, the second concentration gradient can be made independent of the
first concentration gradient. Accordingly, in accordance with the present
invention, gradient index optical elements can be obtained which have
various distribution characteristics that could not ever been thought of
in the prior art. For instance, if a dopant which enhances the refractive
index is selected as the first dopant and a dopant which enhances the Abbe
number is selected as the second dopant, optics having an excellent
chromatic aberration correction ability can be obtained in which .DELTA.n
is sufficiently large and the refractive index and dispersion are of the
type of high refractive index.multidot.low dispersion-low refractive
index.multidot.high dispersion.
It is shown in Japanese Patent Application No. 280897/1989 that in order to
obtain gradient index optical elements of the high refractive
index.multidot.low dispersion-low refractive index.multidot.high
dispersion type which have an excellent chromatic aberration correction
ability, it is only needed to provide concave and convex dependent
multiple distributions by a combination of selected metals in one gradient
index optical elements. According to the present invention, a glass body
having such distributions can be manufactured. In this case, it is
preferable to use at least one metal selected from a group of Ba, La, Sr,
Ca, Ge, Zr, Y and Zn as the first dopant, and at least one or more metals
selected from a group of Ta, Nb, Pb, Ti, Bi, Zn and Zr as the second
dopant, respectively.
In addition, a concentration gradient of the "convex type" means a
distribution in which, if a bar-shaped optic like FIG. 4 (a) is considered
for instance and if the distance r from the center thereof and the ion
concentration are plotted on the abscissa and ordinate, respectively, then
the concentration gradually becomes lower from the center toward the
outside like FIG. 4(b). The concave type is the opposite to this.
Also, it is possible that a metal acting to enhance the refractive index is
selected as the first dopant and a porous body provided with a
concentration gradient by this metal is previously formed, and then a
metal which enhances the refractive index is selected as the second dopant
and a larger concentration gradient is provided to the dopant acting to
enhance the refractive index by dipping the porous body in a solution
containing the second dopant, thereby providing multiple dopings.
As the method for forming a porous body having a first predetermined
concentration gradient due to a first dopant incorporated into the porous
body, the following two are preferably used.
In one method, a wet gel is first created by the sol-gel method using
alcoxide as the raw material for the dopant, and after an appropriate
maturing, the gel has the dopant eluted by an appropriate eluant and is
thereafter dried, thereby obtaining a dry gel which has the concentration
gradient of the first dopant metal in the porous body. The reason for
using alcoxide as the raw material for receiving the dopant here is that,
in the sol-gel method using a metallic salt such as nitrate as the raw
material of the dopant, it is considered that the metallic salt only
deposits between the Si frames and forms a concentration distribution, so
that the dopant distribution provided in the first process collapses
because the dissolution and re-dispersion occur when the dry gel is dipped
in a solvent, whereas for the dry gel synthesized using alcoxide as the
raw material, for receiving the dopant gel combine in the form of Si-O-M
in the gel frame or porous body and are fixed without being eluted by a
conventional solvent, so that the dopant distribution never collapses.
Also, although the dry gel may be used as it is dried, it may also be used
after it is calcinated to strengthen the frame of the gel or porous body.
Further, it may be used in the state of a wet gel before calcinated.
In the other method, a soot having a concentration gradient is obtained as
the dopant metal, which is synthesized by feeding a chloride of SiCl.sub.4
and a dopant metal or the like into an oxygen-hydrogen burner along with a
carrier gas by means of the CVD method (VAD method), and simultaneously
providing a temperature distribution onto a substrate for controlling the
reactivity of the chloride of the dopant metal. A soot is an aggregate of
a fine glass powder synthesized by a gaseous phase reaction. Accordingly,
it has many voids and the metal is vitrified so that it is stably fixed
without being eluted by a conventional solvent.
In the subsequent process, the concentration gradient of a second dopant
different from the obtained first dopant is given into the porous body
which has the first concentration gradient due to the first dopant.
This is somewhat different depending on whether a concave or convex
distribution is provided to the dopant. First, for the provision of a
convex distribution, it is by a very conventional molecular stuffing
method. That is, the porous body obtained in the preceding process is
dipped in the solution of the second dopant and fully stuffed, and
thereafter the porous body is dipped in an appropriate solvent to unstuff
the second dopant, thereby providing the second dopant with a convex
concentration gradient.
Then, for the provision of a concave distribution, first the porous body
obtained in the preceding process is dipped in an appropriate solvent,
thereby sufficiently filling the holes or pores in the porous body with
the solvent. Next, this is dipped in the solvent of the second dopant,
thereby providing the second dopant with a concave concentration gradient.
Incidentally, when the wet gel obtained by the sol-gel method is used, the
"dipping into an appropriate solvent" of the first half can be eliminated.
After providing a concentration gradient to the second dopant, the
distribution fixing and drying are performed, and thereafter the baking is
done to form a dense glass body.
In accordance with the present invention, the dopant within one gradient
index optical element has two independent concentration distributions.
Particularly to use the present invention to obtain a gradient index
optical element having an excellent chromatic aberration correction
ability, it is only needed to make such dopant distributions as shown in
the previously stated Japanese Patent Application No. 280897/1989.
However, as to the doping of a dopant into a porous body, there is a limit
in the amount which can be doped. This is a disadvantage of the molecular
stuffing method, but the reason for this is that the dopant must be
supplied into the holes as a solution and it is largely restricted by the
solubility of the dopant in the solvent. In addition, since the intra-hole
fixing of the dopant depends on the solubility difference by temperature
or that by solvent exchange, it is further restricted. For this, the
latter process which is an application of the molecular stuffing method
preferably takes the distribution that has less doping amount.
Accordingly, a large concentration distribution must be provided to the
dopant in the preceding process. For that, the preceding process is
desirably a gel which has sufficiently large concentration gradient by the
sol-gel method. However, the sol-gel method also has a defect, in which
the distribution provision relies on the elution of the dopant metal, and
thus a convex distribution is easier to produce in principle.
In view of the foregoing, it is most effective that the concentration
gradient of the first dopant is formed in a convex shape by the sol-gel
method using alcoxide as the raw material for receiving the dopant, and
that the concentration gradient of the second dopant is formed in a
concave shape by an application of the molecular stuffing method.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 (a) and (b) are light path diagrams for explaining the relationship
between refractive index and dispersion or radial gradient index optical
elements, respectively;
FIGS. 2 (a) through (d) are light path diagrams for explaining the
relationship between refractive index and dispersion of axial gradient
index optical elements, respectively;
FIG. 3 is a graph showing refractive index - dispersion characteristics;
and
FIGS. 4 (a) and (b) are a perspective view and a graph for explaining a
type of concentration gradient, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(First Embodiment)
5.7 g of zirconium-n-butoxide was dissolved in 18.3 ml of n-butanol
solution and dropped in a solution which was partially hydrolyzed by 12.6
ml of silicon tetramethoxide, 18.3 ml of n-butanol and 1.5 ml of 2N (2
Normality)-hydro-chloric acid, and a mixed solution of 13.7 ml of
n-butanol, 3.9 ml of N-N dimethyl formamide and 22.5 ml of 0.3 N-ammonia
water was dropped in to adjust the sol. This sol was poured in a
polypropylene container having a diameter of 18 mm (.phi.18), which was
sealed and placed in a furnace of 50.degree. C. to set the sol, and
thereafter it was matured as it was.
Then, after it was dipped in sulfuric acid of 3N and given with a
distribution of zirconium, it was dried and a dry gel was obtained which
had a convex concentration gradient in zirconium.
After dipping the dry gel in ethanol to fill the pores of the dry gel with
ethanol, by dipping it in the ethanol solution of titanium chloride for
two hours and again dipping it in diethyl ether, the solvent in the gel
was replaced to cause titanium chloride to separate out in the inner wall
of the gel pores, and the fixing of the distribution was provided and then
it was dried.
The dry gel created by this had a concave concentration gradient of
titanium chloride in the pores while keeping the previous convex
distribution of zirconium.
Finally, when the dry gel was placed in a tubular furnace and heated to
1100.degree. C. for baking, a transparent glass body having no pores were
obtained.
Concentration distributions of zirconium and titanium chloride existed in
the glass body, and the refractive index became lower from the center of
the glass to the perimetry thereof and the Abbe number was also reduced.
This is the characteristics of the direction A in FIG. 3 (decreasing
toward the right-hand side).
(Second Embodiment)
Using SiCl.sub.4 and GeCl.sub.4 as the raw material gas, a soot having a
diameter of 10 mm (.phi.10) was synthesized by the VAD method so that it
was comprised of 85 mol %-SiO.sub.2 and 15 mol %-GeO.sub.2 in the central
composition.
The soot was dipped in water to cause water to fully penetrate into the
inside of the soot, and thereafter dipped in a water solution of
Pg(CH.sub.3 COO).sub.2 of 0.5 mol/l for 50 minutes.
Then, the soot was quickly dipped in acetone of 0.degree. C. to fix the Pb
distribution, and after dried, it was baked, whereby a transparent glass
body was obtained.
The glass body had a convex concentration distribution of Ge and a concave
concentration distribution of Pb in the sinside thereof, and had
dispersion characteristics similar to First Embodiment.
(Third Embodiment)
Yttrium-tripropoxide was dissolved in an appropriate solvent, which was
added to a partially hydrolyzed solution of silicon tetraethoxide and
refluxed and heated for one hour.
A mixed solution of formamide and dilute ammonia water was dropped into
this solution while being stirred, thereby obtaining a sol. This was set
to a gel in a furnace of 60.degree. C. and matured for several days, and
thereafter dipped in 3N-hydrochloric acid to provide a convex
concentration distribution of yttrium in the gel.
The gel was dipped in i-propanol, and after washing the residual salt in
the gel, it was subsequently dipped in an i-propanol solution of titanium
tetra-i-propoxide without being dried, thereby to provide a concave
distribution of titanium in the gel.
Thereafter, the gel was dried and baked to obtain a transparent glass body.
In the glass body, yttrium had a convex concentration distribution and
titanium had a convex concentration distribution, and it had optical
characteristics similar to First Embodiment.
Although the embodiments have been described in consideration of radial
gradient index optical elements, it should be understood that the present
invention can also be applied in axial gradient index optical elements by
changing the shape of the porous body comprised of a gel or soot.
In addition, by the directions of the two distributions same, an optic
having both .DELTA.n's possessed by the respective distributions may be
manufactured, control of the distributions particularly in the outer
perimetry (control of higher degree terms of the distribution factors) may
be made by multiplexing the distributions independently of the directions
of the two distributions.
Thus, a wide variety of optics having various characteristics can be
manufactured.
EFFECT OF THE INVENTION
As described above, in accordance with the method for manufacturing
gradient index optical elements of the present invention, gradient index
optical elements having various characteristics can be obtained which have
not been accomplished only by the simple concentration distribution of a
dopant.
Particularly, refractive index distribution type optics having an excellent
chromatic aberration correction ability can be obtained, in which .DELTA.n
is large enough for practical use and the characteristics change of the
Abbe number is of a high refractive index.multidot.low dispersion-low
refractive index.multidot.high dispersion type.
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